Saruparib in Combination With Physician's Choice of ARPI in Patients With mHSPC Previously Treated With Docetaxel or 177Lu-PSMA Therapy Without Disease Progression and PSA ≥ 0.2 ng/mL (EvoPAR-PR05)

Inclusion Criteria:

* Participant must be ≥ 18 at the time of signing the informed consent.
* Histologically documented diagnosis of prostate adenocarcinoma that is de novo or recurrent and hormone-sensitive.
* Metastatic disease confirmed prior to initiation of previous treatment with docetaxel or Lu-PSMA-containing regimens for mHSPC.
* Previous treatment with docetaxel (IV, Q3w)- or Lu-PSMA (IV, Q6w) with last dose within past 6 months.
* Participants must have the following:

  * Must be receiving ADT with a GnRH analogue or has undergone bilateral orchiectomy.
  * Had no evidence of disease progression
  * Had all toxicities related to docetaxel- or Lu-PSMA-containing treatment (except for alopecia and peripheral neuropathy) resolved to CTCAE Grade 1 or lower.
* PSA ≥ 0.2 ng/mL within 14 days prior to randomization.
* Serum testosterone \< 1.7 nmol/L or 50 ng/dL.
* Palliative radiotherapy for symptoms management will be permitted and is to be completed at least 4 weeks prior to randomization for wide field radiation therapy and at least 2 weeks prior to randomization for limited field radiation therapy.
* Provision of a FFPE tumor tissue sample and a blood sample (for ctDNA).
* Confirmed HRRm, HRD and PTEN status.
* Adequate organ and bone marrow function.
* Minimum life expectancy of 6 months.
* Male, assigned at birth, inclusive of all gender identities.
* Contraceptive use by participants or participant partners should be consistent with local regulations.
* Capable of giving signed informed consent.
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Exclusion Criteria:

* Hypersensitivity to saruparib, ARPI or any excipients of these products or any contraindication or restriction based on the local label.
* Any history of persisting (\> 2 weeks) severe cytopenia due to any cause (eg, ANC\< 0.5 × 10\^9/L or platelets \< 50 × 10\^9/L)
* Any known predisposition to bleeding (eg, active peptic ulceration, recent \[within6 months\] hemorrhagic stroke, proliferative diabetic retinopathy.
* Spinal cord compression or brain metastases unless asymptomatic and stable.
* History of MDS/AML or with features suggestive of MDS/AML
* History of another primary malignancy, with some exceptions.
* Any chronic gastrointestinal diseases or conditions including inability to swallow the formulated product that would preclude adequate absorption of any study drug.
* History of seizure or predispose to seizure, including any history of loss of consciousness or transient ischemic attack within 12 months of enrolment.
* Serious, uncontrolled medical disorder, non-malignant systemic disease or active, uncontrolled infection.
* Major surgical procedure or significant traumatic injury within 4 weeks of the first dose or an anticipated need for major surgery during the study.
* Switched ARPI agent in previous treatment for mHSPC due to disease progression. Note: if the ARPI agent was switched due to any reason other than disease progression and switch was prior to ICF signature, participants will be eligible.
* Any prior treatment with a PARPi or platinum chemotherapy.
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